The present invention relates to format converters and in particular to a system for converting television signals between first and second formats with minimal delay.
Both analog and digital television signals are transmitted or stored in many different standard definition television (SDTV) formats. Analog television signals include three principal formats, NTSC, PAL and SECAM, each of which include one or more sub-formats. Digital television signals may be MPEG encoded or encoded according to the digital video (DV) standard. Each of these standards includes many different formats, having differing numbers of pixels per line, lines per field or frame and fields or frames per second. Thus, in addition to SDTV formats, digital television signals may be encoded in a number of high-definition television (HDTV) formats.
Television studios and, increasingly consumer television viewers, may receive television programming in many different formats. Television studios need to convert the programming into a format that is compatible with their viewers"" equipment. For example, a studio in the United States may receive a Russian program in the SECAM format and need to convert it to NTSC format for transmission to its viewers. Television viewers, on the other hand, need to convert the programming to be compatible with their display devices. For example, a viewer may want to view, on a conventional NTSC television receiver, a program that is broadcast only in high-definition television (HDTV) digital format.
For either of these applications, a television signal in one format is converted into another format by a format conversion process. The process typically involves using scan conversion techniques to change the number of lines per picture, the number of samples per line and the encoding method for the color signals. The result is a television signal having the same content as the input signal but compatible with the desired output standard. It is, of course, desirable for the output signal of the format converter to have the same sharpness and color fidelity as the input signal. In some broadcast systems, timing requirements dictate that these conversions must be performed in less than one frame interval. Application specific integrated circuits (ASICS) have been built which can perform the high quality conversions that are required for these broadcast systems. One such system is described in U.S. Pat. No. 5,587,742 entitled FLEXIBLE PARALLEL PROCESSING ARCHITECTURE FOR VIDEO RESIZING. This system, as with many existing format conversion systems have a minimum delay of at least a one video frame time.
The present invention is embodied in a video format converter that exhibits a delay of less than one video frame time.
An exemplary method of expediting the conversion process is to split an input video stream among two or more format converters. A first portion of each video image is sent to one of the format converters while a second portion of the video image is sent to another format converter. Each format converter begins the conversion process as it receives its input video signal. Thus, the multiple converters operate in parallel. Each converter is synchronized with the other converters to provide its output signal at an appropriate time so that the composite output signal of the multiple converters is a single video signal. The total delay of this format conversion system is less than one video frame interval.
For a better understanding of these and other aspects of the invention, reference may be made to the following detailed description taken in conjunction with the accompanying drawings.